A 2.5-to-4.5-GHz Switched-LC-Mixer-First Acoustic-Filtering RF Front-End Achieving <6dB NF, +30dBm IIP3 at 1×Bandwidth Offset

This paper describes an agile RF front-end that consists of an N-path switched-LC mixer in silicon followed by an acoustic filter - essentially a mixer-first acoustic-filtering RF front-end. The mixer frequency-translates a sharp but fixed acoustic filtering profile to a much higher and LO-defined tunable frequency while preserves input matching, high-linearity, and introduces minimal loss. In contrast to the existing N-path passive-mixer-first receivers which use active baseband filters after N-path switches, using a single acoustic filter as the N-path load is fraught with fundamental challenges. We introduce on-chip LC-tanks to suppress the acoustic filter out-of-band impedance and an all-passive recombination network to share one acoustic filtering among N paths. A front-end prototype using a CMOS switched-LC passive mixer followed by an off-the-shelf 1.6-GHz surface-acoustic-wave (SAW) filter is designed and optimized. In measurement, the RF front-end operates across 2.5-to-4.5 GHz achieving 5.5-dB NF and +29.4-dBm IIP3 at 1×bandwidth offset.